U.S. patent number 4,424,953 [Application Number 06/473,717] was granted by the patent office on 1984-01-10 for dual-layer sintered valve seat ring.
This patent grant is currently assigned to Honda Giken Kogyo Kabushiki Kaisha, Teikoku Piston Ring Co., Ltd.. Invention is credited to Takayuki Matsuda, Setsuo Nii, Takeshi Sugawara, Yoshiaki Takagi.
United States Patent |
4,424,953 |
Takagi , et al. |
January 10, 1984 |
Dual-layer sintered valve seat ring
Abstract
The present invention relates to a dual-layer sintered valve
seat ring having high stiffness and strength. The features of such
ring are: fusion infiltration of Cu into the pores of a ferrous
sintered body; hard alloy particles dispersed in the matrix of the
valve seat body; the composition of the base and the ferrous
sintered body; high density; and, diffusion of an alloying element
of the hard particles around them and into the matrix.
Inventors: |
Takagi; Yoshiaki
(Tsurugashimamachi, JP), Sugawara; Takeshi (Oimachi,
JP), Nii; Setsuo (Chino, JP), Matsuda;
Takayuki (Okaya, JP) |
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha (Tokyo, JP)
Teikoku Piston Ring Co., Ltd. (Tokyo, JP)
|
Family
ID: |
12450325 |
Appl.
No.: |
06/473,717 |
Filed: |
March 8, 1983 |
Foreign Application Priority Data
|
|
|
|
|
Mar 9, 1982 [JP] |
|
|
57-35744 |
|
Current U.S.
Class: |
251/368;
123/188.8; 251/359; 29/890.122 |
Current CPC
Class: |
B22F
7/06 (20130101); C22C 33/0242 (20130101); F01L
3/22 (20130101); F01L 3/02 (20130101); Y10T
29/49409 (20150115); F02B 1/04 (20130101) |
Current International
Class: |
B22F
7/06 (20060101); C22C 33/02 (20060101); F01L
3/00 (20060101); F01L 3/22 (20060101); F01L
3/02 (20060101); F02B 1/04 (20060101); F02B
1/00 (20060101); F01L 003/02 () |
Field of
Search: |
;123/188S ;29/157.1A
;251/368,359 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chambers; A. Michael
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Claims
We claim:
1. A valve seat ring having a high strength and high stiffness and
comprising a valve seat body having a surface in contact with a
valve, and a base for supporting said valve seat body, said valve
seat body and said base consisting of a ferrous sintered article
having a dual-layer structure (hereinafter referred to as the
dual-layer sintered body), wherein: said valve seat body comprises
from 5% to 30% by weight of hard alloy particles having a hardness
of Hv 500 or more and a matrix in which said hard alloy particles
are dispersed and an alloying element of said hard alloy particles
diffuses around said hard alloy particles and into said matrix; a
ferrous sintered body of said base contains from 0.5% to 1.5% by
weight of carbon, from 0.6% to 3.0% by weight of chromium, and at
least one element selected from the group of phosphorus in an
amount of from 0.1% to 0.6% by weight and boron in an amount of
from 0.02% to 0.2%, based on the weight of said ferrous sintered
body; and said dual-layer sintered body has a density of 7.6
g/cm.sup.3 or more and comprises a skeleton, pores formed by
sintering (hereinafter referred to as sintered pores), and copper
or a copper alloy which is fusion-infiltrated into the first
portions of said sintered pores, said skeleton having a density of
from 6.7 g/cm.sup.3 to 7.1 g/cm.sup.3, the percentage of said
sintered pores and the percentage of the second portions of said
sintered pores, in which said copper or copper alloy is not
fusion-infiltrated being 15% or less and 5% or less, respectively,
based on the volume of said dual-layer sintered body.
2. A valve seat ring according to claim 1, wherein said valve seat
body comprises from 10% to 25% by weight of hard alloy
particles.
3. A valve seat ring according to claim 1, wherein said hard alloy
particles contain from 20% to 70% by weight of chromium and
molybdenum.
4. A valve seat ring according to claim 1, wherein said hard alloy
particles contain from 10% to 50% by weight of cobalt and
nickel.
5. A valve seat ring according to claim 1, wherein said carbon is
graphite which is mixed in with raw sintering materials of said
ferrous sintered body.
6. A valve seat ring according to claim 1, wherein said ferrous
sintered body of the base contains from 0.8% to 1.2% of carbon.
7. A valve seat ring according to claim 1, wherein the matrix of
said ferrous sintered body of the base essentially is a pearlite
matrix.
8. A valve seat ring according to claim 1, wherein said chromium is
contained in said ferrous sintered body of the base in the form of
ferrochromium.
9. A valve seat ring according to claim 1, wherein the total
content of said phosphorus and said boron is from 0.12% to 0.6% by
weight.
10. A valve seat ring according to claim 1, wherein the phosphorus
content is from 0.2% to 0.4% by weight and the boron content is
from 0.05% to 0.1% by weight.
Description
The present invention relates to a valve ring of an
internal-combustion engine. More particularly the present invention
relates to a ferrous-sintered dual-layer valve seat ring having an
improved strength and stiffness.
Recently, internal combustion engines have been operated at a high
rotation so as to increase the power thereof. In addition, in order
to reduce the weight of an internal-combustion engine, the weight
of the structual parts is recently being decreased. Thus, the
quality demands for the structual parts, especially the
exhaust-system, of an internal combustion engine become more and
more severe.
It is now described how the power of an internal combustion engine
is increased with regard to design of the cylinder head thereof.
When the diameter of the intake and exhaust valves is increased,
the intake efficiency and exhaust efficiency are increased.
According to one of the methods which are now employed for
increasing the power of an internal-combustion engine, the diameter
of the intake and exhaust values is increased. Due to such an
increase, the inner and outer diameters of valve seat rings is
increased, and, the distance between the intake and exhaust holes
is decreased. If the width of valve seat rings is a constant, the
distance between the intake and exhaust holes considerably
decreases, rendering the cylinder head incapable of withstanding a
thermal load during operation of an internal-combustion engine, and
cracks may form in the cylinder head between the intake and exhaust
holes. It is difficult to increase the diameter of the intake and
exhaust valves because the thickness of conventional valve seat
rings cannot be decreased considerably without decreasing their
inherent strength.
Therefore, it is an object of the present invention to decrease the
thickness of a valve seat ring.
It is another object of the present invention to make the outer
diameter of a valve seat ring such that a satisfactory strength is
imparted to a cylinder head and to increase the inner diameter of a
valve seat ring so as to increase the intake and exhaust efficiency
of an internal combustion engine.
It is a further object of the present invention to improve the
strength and stiffness of a ferrous-sintered dual-layer valve seat
ring, while maintaining the heat-resistance and wear-resistance
which are fundamental properties of a valve-seat ring.
In accordance with the objects of the present invention, there is
provided a valve seat ring having a high strength and high
stiffness and comprising a valve seat body having a surface in
contact with a valve and a base for supporting the valve seat body,
the valve seat body and base consisting of a ferrous sintered
article having a dual-layer structure (hereinafter referred to as
the dual-layer sintered body), wherein: a ferrous sintered body of
the valve seat body comprises from 5% to 30% by weight of hard
alloy particles having a hardness of Hv 500 or more and a matrix,
in which said hard alloy particles are dispersed, and an alloying
element of said hard alloy particles diffusing around said hard
alloy particles and into the matrix; a ferrous sintered body of the
base contains from 0.5% to 1.5% by weight of carbon, from 0.6% to
3.0% by weight of chromium, and at least one element selected from
the group of phosphorus in an amount of from 0.1% to 0.6% by weight
and boron in an amount of from 0.02% to 0.2%, based on the weight
of the ferrous sintered body; and the dual layer sintered body has
a density of 7.6 g/cm.sup.3 or more and comprises a skeleton, pores
formed by sintering (hereinafter referred to as sintered pores),
and copper or a copper alloy which is fusion-infiltrated into the
first portions of the sintered pores, said skeleton having a
density of from 6.7 g/cm.sup.3 to 7.1 g/cm.sup.3, the percentage of
said sintered pores and the percentage of the second portions of
said sintered pores, in which said copper or copper alloy is not
fusion-infiltrated, being 15% or less and 5% or less, respectively,
based on the volume of the dual layer sintered body.
A valve seat ring comprising a valve seat body having a surface in
contact with a valve and a base supporting the valve seat body, the
valve seat body and base consisting of the dual-layer sintered
body, is hereinafter referred to as the dual-layer sintered valve
seat ring.
In the drawings
FIG. 1 is a schematic view of the dual-layer sintered valve seat
ring;
FIG. 2 shows the metal structure of the base at a magnification of
300;
FIG. 3 shows the metal structure of the valve seat body at a
magnification of 300; and
FIG. 4 is a schematic view of a ring-stiffness test.
Conventionally, ferrous-sintered dual-layer valve seat rings have
been manufactured in an attempt to decrease the material cost. That
is, the valve seat body 1a (FIG. 1) is made of a sintered body of
high-alloyed ferrous material, and the base 1b is made of a
sintered body of inexpensive low-alloyed ferrous material.
Sintering of the ferrous materials is an appropriate means of
manufacturing a valve seat ring, because it has a relatively simple
shape, and because various ferrous materials can be selected as the
ferrous-sintered dual-layer valve seat ring.
Before completing the dual-layer sintered valve seat ring according
to the present invention, the present inventors investigated a
conventional ferrous-sintered dual-layer valve seat ring, such as
the one shown in FIG. 1.
According to the present inventors' investigation of a conventional
ferrous sintered dual-layer valve seat ring, since pores are
usually formed on the sintered bodies, the stiffness
characteristics for examples, the Young's modulus, thereof are not
excellent.
The present inventors therefore recognized necessity of sealing the
pores mentioned above. In addition, in a conventional ferrous
sintered dual-layer valve seat ring, the stiffness and strength of
the base 1b are lower than those of the valve seat body 1a. The
present inventors therefore also recognized necessity of increasing
the stiffness and strength of the base 1b to values equivalent to
or greater than those of the valve seat body 1a.
The present invention is described in detail with regard to: (1)
the composition of the valve seat body, (2) the composition of the
base, (3) the method of compacting powders, (4) the skeleton
density of the dual layer sintered body, (5) the fusion
infiltration of copper or copper alloy, and (6) the metal
structure.
Composition of the Valve Seat Body: Hard alloy particles are very
wear-resistant and enhance the wear resistance of the valve seat
body. Since an alloy element of hard alloy particles diffuses
around the hard particles and therefore, is diffused in the matrix
of the valve seat body the heat resistance of the matrix is
increased. The diffused alloy element stengthens the bond between
the hard alloy particles and the matrix, with the result that the
strength of the valve seat body is increased.
The hard alloy particles must have a hardness of at least Hv 500 so
that the hardness is at least equal to the hardness of a valve.
When the amount of hard alloy particles is less than 5% by weight,
the particles are not effective for enhancing the wear resistance
of the valve seat body. When the amount of hard alloy particles is
more than 30%, cracks may form during compacting of the raw
sintering powders, the life of dies used for compacting the raw
sintering powders short, and the change in dimension of a green
compact is excessively great during sintering. It is preferred that
the valve seat body comprises from 5% to 30%, preferably from 10%
to 25%, by weight, of hard alloy particles.
Hard alloy particles can be easily obtained by casting a high alloy
material, such as a Fe-C-Cr-Mo-Co-Ni alloy, crushing the cast body,
and adjusting the grain size of the resultant powder. The C, Cr,
and Mo of the alloy mentioned above mainly promote enhancement of
the wear resistance, and the Co and Ni mainly promote enhancement
of the heat-resistance.
It is preferred that the hard alloy particles contain from 20% to
70% by weight of chromium and molybdenum. It is preferred that hard
alloy particles contain from 10% to 50% by weight of cobalt and
nickel. Molybdenum and chromium, as well as cobalt and nickel can
be optionally selected within the above-mentioned ranges.
It is preferred that the above-mentioned carbon of from 0.5% to
1.5% by weight mentioned above be graphite which is mixed in with
the raw sintering materials. The graphite should be mixed by weight
with the raw sintering materials in an amount of from 0.8 part to
1.2 parts by weight with the proviso that iron powders are 100
parts. The graphite strengthens the matrix of the valve seat
body.
Usually, the raw sintering materials consist of hard alloy
particles, graphite powder, and an iron powder, which are mixed at
an amount of from 5% to 30%, from 0.5% to 1.5%, and the balance
being the iron powder, respectively.
The raw sintering materials which are used for producing skeleton
of the valve seat body of the dual layer-sintered body is
hereinafter referred to as the valve seat body powder.
Composition of the Base: The base carries the valve seat body and
therefore makes it possible to reduce the amount of expensive
alloying elements. Since the base according to the present
invention must have a stiffness and strength which are equivalent
to or greater than to those of the valve seat body, the ferrous
sintered body of the base contains from 0.5% to 1.5% by weight of
carbon, from 0.6% to 3.0% by weight of chromium, and at least one
element selected from the group of phosphorus in an amount of from
0.1% to 0.6% by weight and boron in an amount of from 0.02 to 0.2%
by weight.
Carbon renders the matrix of the ferrous sintered body of the base
essentially pearlitic and enhances the strength of the matrix. When
the amount of carbon is less than 0.5% by weight, ferrite is liable
to form in the matrix of the ferrous sintered body, thereby
reducing its strength. When the amount of carbon is more than 1.5%
by weight, cementite is liable to form in the matrix of the ferrous
sintered body of the base and is liable to embrittle.
Chromium is preferably contained in the ferrous sintered body in
the form of ferrochromium, and, the ferrochromium phases are
preferably dispersed in the ferrous sintered body of the base. The
dispersed chromium-containing phases, such as the dispersed
ferrochromium phases, bring about the so-called dispersion
hardening and enhance the strength of the base. When the amount of
chromium is less than 0.6% by weight, chromium is not effective for
strengthning the base. When the amount of chromium is more than
3.0% by weight, strengthening of the base is not marked as compared
with that attained when the amount of chromium is 3.0% by weight or
less. In addition, it is economically disadvantageous to
incorporate into the ferrous sintered body more than 3% by weight
of chromium.
When not only chromium but also molybdenum, tungsten, and/or
vanadium are incorporated in the form of a ferroalloy into the
ferrous sintered body, dispersion-hardening can also be brought
about.
Since phosphorus and boron form the Fe-P-C eutectic structure and
the Fe-B-C eutetic structure, respectively, in the sintered Fe-C
alloy, phosphorus or boron is conventionally used to enhance the
wear resistance of ferrous sintered bodies. In the present
invention, phosphorus and/or boron are used in a relatively small
amount so as to prevent fomation of the eutectic structure and to
generate minute liquid phases at numerous sites of the
ferrous-sintered body of the base and thus to locally diminish and
spheroidize the pores. When the minute liquid phases solidify, the
ferrous sintered body of the base tends to shrink, and thus the
solidifying minute liquid phases tend to suppress expansion of the
ferrous sintered body during the fusion infiltration of copper or a
copper alloy. If the ferrous sintered body of the base expands
during the fusion, not only the density of the base is decreased,
but also the dimensional accuracy of the base is impaired. Since
phosphorus and/or boron are used in the present invention as an
element(s) of the base, base having a high density, high stiffness,
and a high dimensional accuracy can be obtained.
Phosphorus and/or boron are partially dissolved in the matrix of
the ferrous sintered body of base and strengthen it.
When the amount of phosphorus is less than 0.1% by weight and when
the amount of boron is 0.02% by weight, phosphorus and boron are
not effective for increasing the density and and for strengthening
the matrix of ferrous sintered body of the base. When the amount of
phosphorus is more than 0.6% by weight, and when the amount of
boron is more than 0.2% by weight, the amount of liquid phases is
so great that a Fe-P-C eutectic or a Fe-BC eutectic structure is
formed, and, further the ferrous-sintered body of the base
embrittles.
It is preferred that the total amount of phosphorus and said boron
be from 0.12% to 0.6% by weight and that the phosphorus amount, and
the boron amount are from 0.2% to 0.4% by weight, and from 0.05% to
0.1% by weight, respectively.
The raw sintering materials for producing the base are usually an
iron powder, a ferrochromium powder, a ferroboron powder, a
ferrophosphorus powder, and a graphite powder. These powders are
mixed together predetermined amounts. The ferroalloys may be those
stipulated under the following Japanese Industrial Standard
(JIS):
JIS G 2303 (ferrochromium);
JIS G 2318 (ferroboron); and,
JIS G 2310 (ferrophosphorus).
The ferrophsphorus and ferroboron powders are preferably in the
form of fine particles 10 .mu.m or less in size so that they can be
uniformly distributed and to prevent phosphorus and boron from
segregating and generating the eutectic structure.
Compacting the Powders: The base powder and the valve seat body
powder are loaded into metal die in such a manner that these two
powders form a dual layer. The base powder and the valve seat body
powder are simultaneously subjected to compacting. The weight or
volume proportion of the base powder to the valve seat body-powder
is determined based on the proportion of the base to the value seat
body in the dual-layer sintered valve seat ring, and the latter
proportion is determined by the characteristics of an internal
combusion engine. The density of a green compact, i.e., the
compacted base powder and valve seat body powder, virtually
determines the skeleton density and pore percentage of the
dual-layer sintered body. Such compacting must therefore be carried
out under such a pressure that the density of the skeleton of the
dual-layer sintered body throughout the body is 6.7 g/cm.sup.3 to
7.1 g/cm.sup.3, and that the percentage of the sintered pores of
the dual layer sintered body is 15% or less. When the density of
the green compact is from 6.75 g/cm.sup.3 to 7.15 g/cm.sup.3, the
skeleton has the density of from 6.7 g/cm.sup.3 to 7.1
g/cm.sup.3.
Skeleton Density: The density of skeleton of the dual-layer
sintered body is from 6.7 g/cm.sup.3 to 7.1 g/cm.sup.3, and the
dual-layer sintered body includes the sintered pores in an amount
of from 15% or less. The density of the skeleton mentioned above is
relatively high in the sintered ferrous articles because of the
reasons explained in the following paragraph. The base powder and
the valve seat body powder may be mainly comprised of reduced
ferrous powder but preferably are mainly comprised the atomized
powders since atomized powders have excellent compacting
characteristics. The density of the skeleton should be uniform
through the dual-layer sintered body. This can be achieved by
utilizing a base powder and a valve seat body powder having
virtually the same grain size and compacting characteristics. When
the green compact is sintered, the dual-layer sintered body having
the skeleton density and pores mentioned above are obtained. The
sintering is preferably carried out at a temperature of from
1080.degree. C. to 1150.degree. C. in a reducing atmosphere for a
period of from 30 to 60 minutes. The reducing atmosphere may be
prepared by decomposing an ammonia gas or the like.
Fusion infiltration: The dual-layer sintered body is subjected to
fusion infiltration of the sintered pores. Copper or a copper alloy
is used for the fusion infiltration. The element used for fusion
infiltration is hereinafter referred to as copper unless otherwise
specified. Essentially all of the sintered pores other than
isolated sintered pores are fusion infiltrated with copper.
When the first portions of the sintered pores, i.e., essentially
all of the sintered pores other than the isolated sintered pores,
are fusion infiltrated, and thus sealed, the stiffness is enhanced.
Not only is the stiffness is enhanced, the bond between the base
and the valve seat body is strengthened. Copper seems to strengthen
the bonding by sealing the sintered pores which are present on the
bonded surfaces of the base and the valve seat body, and, by
bringing about diffusion between the base, and the valve seat
body.
Since copper has an excellent thermal conductivity, the copper
fusion infiltration in the first portions of the sintered pores
reduces the thermal load during operation of an internal combustion
engine and enhances the durability of the dual-layer sintered valve
seat ring. It suppresses the creep deformation of the dual-layer
sintered valve seat ring.
When the skeleton density is less than 6.7 g/cm.sup.3 or when the
percentage of the sintered pores is more than 15%, the amount of
the fusion-infiltration copper becomes excessively large and the
stiffness of the dual-layer sintered valve seat ring becomes low.
When the density of the skeleton is more than 7.1 g/cm.sup.3, the
fusion-infiltration of copper is not effective for enhancing the
stiffness, and the like.
For the fusion infiltration, both copper, and a copper alloy, such
as a Cu-Fe-Mn alloy, a Cu-Fe-Mn-Zn alloy, or a Cu-Co-Zn alloy, may
be used. The copper is located on the dual layer sintered body and
is then infiltrated. Alternatively, the dual-layer sintered body
may be dipped in the copper bath. Fusion-infiltration is carried
out at a temperature of from 1080.degree. to 1150.degree. C. When
the copper is located on the dual layer sintered body, and is then
infiltrated, the amount of copper is preferably from 13% to 18% by
weight based on the total weight of the dual layer sintered valve
seat ring. Part of the copper is lost during the fusion
infiltration, and part of it is fusion-infiltrated into the
sintered pores.
The dual-layer sintered valve seat ring, i.e. the
copper-infiltrated dual-layer sintered body, must have density of
7.6 g/m.sup.3, or more, and the second portions of the sintered
pores, that is the sintered pores into which the copper is not
infiltrated, must be 5% or less.
The sintering and fusion-infiltration of copper may be
simultaneously carried out.
Metal Structure: The metal structure of the base is discribed with
reference to FIG. 2. In FIG. 2, A denotes the pearlite matrix, in
which the boron and phosphorus are solid-dissolved. B denotes the
ferrochromium particles which are uniformly distributed in the
pearlite matrix A. C denotes the fusion-infiltrated copper which
seals the first portions of the sintered pores. The continuous
sintered pores are sealed by the fusion-infiltrated copper C, as is
shown in FIG. 3. The base shown in FIG. 2 has a higher strength
than a base having a plain pearlite matrix, because the
ferrochromium particles B achieve the dispersion hardening, and
further the boron or phosphorus is solid-dissolved in the pearlite
matrix A and strengthens the matrix A.
The metal structure of the valve seat body is described with
reference to FIG. 3. In FIG. 3, the symbol D denotes a martensite
matrix, and the E denotes the hard alloy particles. The matrix has
the martensite structure, because nickel, chromium, and molybdenum
diffuse around the hard alloy particles E and into the matrix, and,
further the fusion-infiltrated copper C diffuses into the matrix.
The nickel, copper and the like form a solid solution in the
matrix.
According to a comparative experiment carried out by the present
invention, when the valve seat body was not subjected to the
fusion-infiltration of copper, the matrix structure of the valve
seat body was not martensitic.
It is therefore believed that the fusion-infiltration copper
enhanced the diffusion of the alloy elements of hard alloy
particles around them. It is to be noted that rapid cooling after
fusion-infiltration of copper is not indispensable for forming the
martensite matrix, and, thus air cooling is sufficient for forming
a martensite matrix. A tempared martensite matrix (not shown in the
drawings) is obtained when, after sintering the dual layer sintered
valve seat ring is tempered. The martensite matrix and tempered
matrix have a hardness of from Hv 500 to 700, and from Hv
300.about.500, respectively.
The base and the valve seat body may be formed concentrically and
form the outer and inner parts, respectively, of the dual layer
valve seatring.
EXAMPLES
The present invention is described with reference to the examples
and the comparative examples. In these examples, the percentage is
based on weight except for percentage of pores. In these examples
and the comparative examples, the valve seat body powders was
prepared by mixing the following (a), (b), and (c) in an amount so
that the composition of the valve seat body given in Table 1 is
obtained, and then adding into the mixture 0.8% of zinc
strearate:
(a) the hard alloy particles: the crushed powder of -100 mesh,
containing 2% of C, 20% of Cr, 8% of Ni, and 20% of Mo, 34% Co, the
balance being Fe, and having the hardness was from Hv 700 to
800;
(b) the iron powder: the -100 mesh atomized powder; and,
(c) the carbon powder: -325 mesh graphite powder.
The base powder was prepared by mixing the followings (a) through
(e) with each other so as to give the composition of the base given
in Table 1, and then adding into the mixture 0.8% of zinc
stearate;
(a) -150 mesh atomized iron powder;
(b) -100 mesh ferrochromium powder (60% Cr);
(c) 10 .mu.m or less of ferrophosphorus powder (25% P);
(d) 10 .mu.m or less of ferro boron powder (20% B); and,
(e) -325 mesh graphite powder
The proportion of the base powder and the valve seat body-powder
was selected so that the base and the valve seat body have the same
height as each other. The base powder and the valve seat
body-powder were successively loaded in a metal die so as to form a
dual layer, and these powders were simultaneously compacted. The
obtained green compact was sintered at 1130.degree. C. for the
period of 40 minutes in decomposed ammonia gas. Simultaneously with
sintering, fusion infiltration was carried out. Copper alloy used
for the fusion infiltration contained 3.8% of Fe, 2.2% of Mn, and
2.2% of Zn, the balance being Cu.
The dual-layer sintered valve seat rings were tempered at
700.degree. C. for the period of one hour and then air cooled. The
dual-layer sintered valve seat rings had an outer diameter of 31
mm, an inner diameter of 25 mm, and a height of 7 mm. These valve
seat rings were subjected to measurement of stiffness.
The stiffness was measured as shown in FIG. 4. A constant load of
100 kgf was applied to each dual-layer sintered valve seat ring 1
in a radial direction by means of plates 2 and 3 and the deflection
of such ring was measured. The smaller the deflection, the greater
the stiffness.
Samples for measuring the tensile strength and Young's modulus were
prepared. The samples comprised dual-layer base and valve seat body
portions. Tensile stress was applied in a direction perpendicular
to the dual layers.
The Young's modulus was obtained using the tensile stress and
strain which did not exceeding the elastic limit.
The results of measurement are given in Table 1.
TABLE 1
__________________________________________________________________________
Skel- Valve Seat Body Powder eton Density Stiffness Hard Den-
Amount of After Tensile Young's of Rings Alloy- sity Cu-Fusion
Infil- Strength Modulus (Deflec- Particles C C Fe Base Powder (%)
(g/ Infiltration tration (kg/ (kg/ tion) Examples (%) (%) (*) (%)
Cr P B C Fe cm.sup.3 ) (%) (g/cm.sup.3) mm.sup.2) mm.sup.2) (mm)
__________________________________________________________________________
1 5 1.0 0.95 bal 0.6 0.1 -- 1.0 bal 6.7 18 7.7 76 17500 0.21 2 5
1.0 0.95 bal 0.6 -- 0.02 1.0 bal 6.7 18 7.7 77 18000 0.20 Inven- 3
15 1.0 0.85 bal 1.5 0.3 -- 1.0 bal 6.9 16 7.8 80 18400 0.20 tion 4
15 1.0 0.85 bal 1.5 -- 0.1 1.0 bal 6.9 16 7.8 81 18600 0.19 5 30
1.0 0.70 bal 3.0 0.6 -- 1.0 bal 7.1 13 7.8 83 19500 0.19 6 30 1.0
0.70 bal 3.0 -- 0.2 1.0 bal 7.1 13 7.8 85 19200 0.18 7 15 1.0 0.85
bal 1.5 0.2 0.05 1.0 bal 6.9 16 7.8 84 19000 0.18 1 30 1.0 0.70 bal
3.0 0.3 0.1 1.0 bal 7.1 -- -- 38 13900 0.30 Compar- 2 20 1.0 0.80
bal 3.0 -- -- 1.0 bal 6.9 16 7.8 65 14700 0.27 ative 3 20 1.0 0.80
bal -- 0.3 -- 1.0 bal 6.9 16 7.8 66 15500 0.25 Exam- 4 20 1.0 0.80
bal -- -- 0.2 1.0 bal 6.9 16 7.8 63 14900 0.28 ples 5 20 1.0 0.80
bal 3.0 0.3 0.1 1.0 bal 6.5 20 7.8 61 15900 0.25 6 20 1.0 0.80 bal
3.0 0.3 0.1 1.0 bal 6.5 -- -- 32 11300 0.35
__________________________________________________________________________
Note: *Weight part based on iron powder of 100 parts.
In comparative example 1, the fusion-infiltration was not carried
out. In comparative example 2, the base did not contain phosphorus
and boron. In the comparative examples 3 and 4, the base did not
contain chromium. In the comparative example 5, the skeleton
density was low. In the comparative example 6, the skeleton density
was low and the fusion-infiltration was not carried out. As is
clear from Table 1, the stiffness of the examples 1.about.7 is
superior to that of the comparative examples 1.about.6.
The dual-layer valve seat rings of the examples 1, 4, 5, and 7, and
of the comparative examples 1, 2, 5, and 6 were mounted on the
Al-alloy cylinder head of a water-cooled OHC gasoline-engine having
four cylinders and total displacements of 1600 cc. The above
mentioned four comparative examples correspond to the conventional
ferrous sintered dual layer valve seat rings.
The durability of dual-layer valve seat rings used as exhaust
valves seats was tested at 5,000 rpm and under a full load of the
gasoline engine fou 400 hours. The fuel gasoline was no-lead
gasoline.
The average amount of wear of the four dual-layer valve seat rings
was obtained by measuring the variance in the tappet
clearances.
The result are given in Table 2.
TABLE 2 ______________________________________ Average Wear Amount
(mm) ______________________________________ Examples 1 0.06 Example
4 0.05 Example 5 0.035 Example 7 0.05 Comparative Example 1 0.04
Comparative Example 2 0.05 Comparative Example 5 0.05 Comparative
Example 6 0.05 ______________________________________
As is clear from Table 2, the wear resistance of the dual layer
valve seat rings according to the present invention is comparable
to that of conventional dual layer valve seat rings.
* * * * *